The present invention relates to a cosmetic composition consisting of a dispersion of small lipid spheres. Aqueous dispersions of this type have already been described in British Patent 1,539,625.
The small lipid spheres in these dispersions are in the form of roughly concentric laminae consisting of two or more lipid layers which are separated from one another by layers of an aqueous phase. They can thus be used to encapsulate water-soluble active substances, for example, pharmaceutical or cosmetic substances, in the aqueous compartments between the lipid layers, and to protect them from the exterior.
The above mentioned British patent also describes a new process for the preparation of an aqueous dispersion of small lipid spheres, which consists firstly in bringing the lipids which are to constitute the concentric laminae of the small spheres into contact with the aqueous solution to be encapsulated, the lipophilic/hydrophilic ratio of the chosen lipids being such that the latter swell in water or in the aqueous phase to be encapsulated, in order to form a plane lamellar phase; secondly in adding, to the lamellar phase, an aqueous solution which is to constitute the continuous external phase of the dispersion; and thirdly in subjecting the whole to vigorous agitation order to obtain a dispersion of small spheres, between the concentric laminae of which the aqueous phase to be encapsulated is trapped.
In order to form the concentric laminae of the small spheres, it is possible, according to the teaching of this British patent, to use either ionic or nonionic amphiphilic lipids. The following are preferred amongst the nonionic amphiphilic lipids:
a straight or branched-chain polyglycerol ether of the formula: ##STR1## wherein
n has a statistical mean value of from 1 to 6 and
R is a straight or branched-chain saturated or unsaturated, aliphatic group containing 12 to 30 carbon atoms, a hydrocarbon group of a lanolin alcohol or a 2-hydroxyalkyl residue of a long-chain .alpha.-diol,
a straight or branched chain polyglycerol ether containing two fatty chains;
a polyglycerol ester of a straight chain fatty acid;
a polyoxyethylenated fatty alcohol;
a polyoxyethylenated sterol;
an ether of a polyhydric alcohol;
an ester of a polyhydric alcohol which can optionally be oxyethylenated;
a glycolipid of natural or synthetic origin;
a hydroxyamide of the formula ##STR2## alkyl or alkenyl group, R.sub.2 is a saturated or unsaturated C.sub.7 -C.sub.31 hydrocarbon group, and wherein B is a group derived from a mono- or polyhydroxylated primary or secondary amine and R.sub.3 is hydrogen, methyl, ethyl or hydroxyethyl, or (ii) --COOZ wherein Z is a residue of a C.sub.3 -C.sub.7 polyhydric alcohol.
Amongst the cosmetic active substance which can be encapsulated in the small lipid spheres, the above-mentioned British patent gives as examples substances for skin care, such as humectants, artificial tanning agents, skin-coloring agents, water soluble sun filters, antiperspirants, deodorants, astringents, freshening-up products, tonics, cicatrising agents, keratolytic agents, depilatories, perfumed waters and extracts from animal or plant tissues.
It has been observed that the cosmetic compositions referred to above, in the form of an aqueous dispersion of small lipid spheres, exhibit the advantage, compared with conventional preparations in the form of an of and water emulsion, of having a less aggressive action and consequently of causing less irritation when they are applied to the skin.
The aim of the present invention is to provide a cosmetic composition based on an aqueous dispersion of small lipid spheres, which makes it possible to combine the advantages of the dispersions of small spheres with the advantages resulting from the presence of cosmetic oils.
The present invention thus provides a cosmetic composition consisting of an aqueous dispersion of small spheres composed of organized molecular layers between which an internal aqueous phase is encapsulated, these layers consisting of at least one nonionic amphiphilic lipid, in which at least one oil is dispersed in the external aqueous phase which surrounds the small spheres, the said oil comprising fatty acid total esters of polyols, especially liquid triglycerides, and fatty acid esters of branched alcohols, of the formula R--COOR', in which formula R represents the radical of a higher fatty acid, which fatty acid contains from 8 to 20 carbon atoms and R' represents a branched hydrocarbon chain containing from 3 to 20 carbon atoms.
It has been observed, unexpectedly, that the small spheres of nonionic amphiphilic substances make it possible to stabilize the oil-in-water dispersion without requiring the addition of a surface active emulsifying agent and without causing the destruction of the small spheres. It is known from Harry's Cosmeticology, 6th Edition Vol. I, page 703, that surface active agents provide the majority of the emulsifying agents used in cosmetic emulsions; the stability of the emulsifying agents depends mainly on the presence of such emulsifiers having hydrophobic and hydrophilic moieties, the molecules of which are adsorbed onto the surface of the oil droplets to form a kind of continuous membrane which prevents direct contact between two adjacent droplets, for example, during shock. Thus in the present case, those skilled in the art might have expected that the nonionic amphiphilic lipids in the small spheres would act as an emulsifier by being adsorbed onto the surface of the oil droplets, but they would also have expected that this stabilization effect would also have the effect of causing the destruction of the concentric laminae of the small spheres. This has been found not to be the case at all and, surprisingly, the small spheres of nonionic amphiphilic substances of the invention are capable of stabilizing a dispersion of at least one vegetable oil, defined above, in an external aqueous phase by dispersing around the oil droplets while retaining their integrity.
As known from Harry's Cosmeticology, referenced above, at pages 701 and 702, hydrocolloids, i.e. substances yielding gel with water, such as plant gums and gelling polymers, are inefficient as primary emulsifier, although they are very useful as secondary stabilizers in oil-in-water lotions and semi-solid creams. They generally function merely through thickening the aqueous phase but have been reported to concentrate at the interface to form interfacial films.
U.S. Pat. No. 3,957,971 describes dispersions of small spheres of ionic amphiphilic substances or liposomes, which are used in cosmetic creams or lotions, that is to say, in water-in-oil or oil-in-water emulsions. In the present invention, the small spheres are composed not of ionic amphiphilic substances, but of nonionic amphiphilic substances. Moreover, it can be shown that the liposomes do not make it possible to stabilize a dispersion, in water, of a vegetable oil as defined above, whereas, totally unexpectedly, the small spheres of nonionic amphiphilic substances of the invention do make it possible to stabilize a dispersion of this type.
The cosmetic composition according to the invention can be prepared in two or more stages; in a first stage, an aqueous dispersion of small spheres is prepared from nonionic amphiphilic lipids using either the process described in British Patent 1,539,625 or the procedures described in French Patent 2,221,122, the disclosures of which are hereby incorporated by reference. In a second stage, once the aqueous dispersion of small spheres has been produced, the oil is added thereto. The oil is then dispersed in the external aqueous phase by agitation.
Preferably, the cosmetic composition according to the invention contains from 2 to 10% or even from 0.5 to 20% of nonionic amphiphilic lipid(s) which form the walls of the small spheres, and from 2 to 40% or even from 0.5 to 40% of dispersed , oil ( s ), these percentages being expressed by weight, relative to the total weight of the composition. Advantageously, the ratio by weight of nonionic amphiphilic lipid ( s ) , relative to the dispersed oil (or oils), is from 0.2:1 to 1:1 or even from 1:40 to 40:1.
The oils which are incorporated into the composition according to the invention are fatty acid total esters of polyols, in particular liquid triglycerides, and fatty acid esters of branched alcohols, of the formula: R-COOR' in which formula R represents the radical of a higher fatty acid, which fatty acid contains from 8 to 20 carbon atoms and R' represents a branched hydrocarbon chain containing from 3 to 20 carbon atoms. Suitable fatty acid total esters of polyols include sunflower oil, corn oil, soya oil, gourd oil, grapeseed oil, and glycerol tricaprocaprylate. Purcellin oil may be mentioned specifically as a higher fatty acid ester of a branched alcohol.
Other vegetable oils usefully employed in the present invention include cocoa butter oil, dog-rose oil, black currant oil, Ximenia Americana oil, Pentacletra Macrophyla oil, Voandzeia oil, black currant obtusifolia oil, Trichilia. Emetica oil, Pongamia Glabra oil, passion-flower oil, tomato seed oil, macadamia oil, sesame oil and jojoba oil.
The cosmetically active substance of the composition according to the present invention can be encapsulated inside or outside the small spheres. Thus, in a preferred embodiment, the oily phase of the composition contains one or more liposoluble cosmetic substances. In the preparation of the composition according to the invention, these substances are dissolved beforehand in the oil which is to be added to the dispersion of small lipid spheres. Representative liposoluble active cosmetic substances include, in particular, anti-sunburn filters such as 2-ethylhexyl para-dimethylaminobenzoate, or substances for improving the condition of dry or old skin, in particular, unsaponifiable substances such as those derived from soya and from avocado, tocopherols, vitamins E and F and antioxidants.
The oil-in-water dispersion which constitutes the external medium of the dispersion of small spheres can contain at least one additive, in particular a gelling agent or perfume. The additive can be added to the dispersion at the same time as the oil. The gelling agent can be introduced at a concentration of, say 0.1 to 2%, these percentages being expressed by weight, relative to the total weight of the composition. Amongst the gelling agents which can be used, there may be mentioned cellulose derivatives such as hydroxyethylcellulose, synthetic polymers, algae derivatives such as satiagum, and natural gums such as tragacanth. Hydroxyethylcellulose, a mixture of carboxyvinylic acids commercially available under the name "CARBOPOL 940", satiagum and tragacanth are preferably used as gelling agents.
The nonionic amphiphilic lipids which are to constitute the concentric laminae of the small spheres in the cosmetic composition according to the invention are typically:
straight or branched chain polyglycerol ethers having the following formulae: ##STR3## wherein n is a statistical average value from 2 to 6 and R represents a straight or branched saturated aliphatic chain containing from 16 to 20 carbon atoms or the hydrocarbon radical of a lanolin alcohol;
straight or branched polyglycerol ethers containing two fatty chains;
polyglycerol esters of a straight chain fatty acid; and
polyoxethylenated sterols.
At the moment of formation of the plane lamellar phase obtained by bringing the nonionic amphiphilic lipids into contact with the aqueous phase to be encapsulated, various auxiliary agents can be associated with the said lipids in order to modify, for example, the permeability or the surface charge of the small spheres. For this purpose, there may be mentioned the optional addition of long-chain alcohols and diols, sterols, in particular cholesterol and .beta.-sitosterol, long-chain amines and their quaternary ammonium derivatives, in particular didodecyldimethylammonium bromide, hydroxyalkylamines, polyoxyethylenated fatty amines, long-chain aminoalcohol esters. and their salts and quaternary ammonium derivatives, phosphoric acid esters of fatty alcohols, in particular dicetyl phosphate, alkyl-sulphates, for example sodium cetyl-sulphate, and certain polymers such as polypeptides and proteins.
Apart from the auxiliary agents listed above, it is possible to add a preservative such as methyl parahydroxybenzoate.
The aqueous phase, whether internal or external, can contain a water-soluble cosmetic substance normally used for the care of the face, the hands or the body. Amongst these substances, there may be mentioned humectants such a glycerol, sorbitol, pentaerythritol, inositol and pyrrolidonecarboxylic acid and its salts, artificial tanning agents such as dihydroxyacetone, erythrulose, glyceraldehyde and .gamma.-dialdehydes such as tartaraldehyde, skin-coloring agents, sun filters, antiperspirants, deodorants, astringents, freshening-up products, tonics, cicatrising agents, keratolytic agents, depilatories, perfumed waters, extracts from animal or plant tissues, such as proteins, amniotic liquid and polysaccharides, and antiseborrheic agents.